Conventionally, there has been proposed a technique in which the directivity of sound signal propagation is controlled by forming a sound beam using a plurality of speakers which are arranged in an array fashion (for example, refer to Patent Document No. 1). The utilization of this technique obviates the necessity of placing a plurality of speakers on the periphery of a user (a listener) as in the case with a conventional surround sound system and enables the reproduction of surround sound using a single panel made up of the array of speakers.
FIG. 4 is a top perspective view of a room in which the speaker system described in Patent Document No. 1 is set, which shows an example in which a 5.1-channel surround sound system is configured by a speaker system having an array of speakers. A speaker system 113 shown in FIG. 4 includes several tens to several hundreds of speaker units which are arranged into a predetermined array on a single panel, emits beams of surround sound by adjusting an output timing of surround sound from each speaker unit for every channel and implements a delay control so that the beams focus on wall surfaces. Then, the sound of each channel is made to be reflected on the ceiling or wall so as to be diffused to thereby produce a sound source on the wall, whereby a sound field of multiple channels is reproduced. As shown in FIG. 4, the speaker system 113, which is disposed at a lower portion of a video system 112 which is set in the vicinity of a central portion of a wall 120 of the room and in front of a user U, outputs directly to the user sounds similar to those produced by a center speaker (C) and a low frequency supplementing woofer (LFE). In addition, the speaker system 113 causes the beams to be reflected on walls 121, 122 which lie left and right to the user U so as to produce an R-channel speaker 114 and an L-channel speaker 115. Furthermore, the speaker system 113 causes the beams to be reflected on a ceiling 124, the walls 121, 122 which lie left and right to the user and a wall 123 which lie behind the user U so as to produce an SR-channel speaker 116 and an SL-channel speaker 117 which lie rear left and right of the user U. Thus, in the surround sound system of the array of speakers, the sound signal of each channel is delay controlled so as to be converted into the beam of sound, and the beams of sound so converted are then caused to be reflected on the walls so as to produce the plurality of sound sources, so that a surround-sound effect can be obtained which would be realized by setting a plurality of speakers on the periphery of the user U.
Here, in this description, in the 5.1-channel surround sound system, a front left channel is denoted by L (Left), a front right channel by R (Right), a center channel by C (Center), a rear left channel by SL (Surround Left), a rear right channel by SR (Surround Right), and a subwoofer by LFE (Low Frequency Effects).
Patent Document No. 1: JP-T-2003-510924 (the term “JP-T” as used herein means a published Japanese translation of PCT patent application)
FIGS. 5A, 5B are top perspective views which show an example in which the speaker system is set in a rectangular parallelepiped-like room which differs largely in dimension between width and depth. When listening to sound from the speaker system described in Patent Document No. 1, there occurs a case where sound is wanted to be reproduced in a stereo mode of only the front system channels (L, R (and C) or two channels including the surround channel. In addition, there also occurs a case where a stereo source is not converted into a beam but is wanted to be reproduced as a normal stereo sound.
For example, in the event that the speaker system of Patent Document No. 1 is set in the vicinity of an end portion of the rectangular parallelepiped-like room which differs largely in dimension between width and depth, as shown in FIG. 5A, since a distance from the speaker system to the wall lying left thereto is different from a distance from the speaker system to the wall lying right thereto, the spreading out effect of surround sound becomes excessive, and the density effect and orientation effect are deteriorated in sounds of, in particular, the front channels (L, R (and C)). Then, as this occurs, as shown in FIG. 5B, the sound of each channel is not converted into a sound beam but is converted into a stereo sound so as to preferably be reproduced as a normal stereo sound.
The speakers of the speaker system (the array of speakers) are allocated at a central portion of the system to a reproducing region for the L channel and a reproducing region for the R channel so as to reproduce sound from the speaker system as stereo sound using all the speakers, however, since a frontal directivity is generated in medium and high frequencies irrespective of outputting sound signals of the relevant channels simultaneously without implementing a delay control thereon, a sound image results which is far from the normal stereo effect. Due to this, there has existed a problem that the reproduction of stereo sound using all the speakers of the speaker system described in Patent Document No. 1 is not preferable.